With the proliferation of light-emitting-diode (LED) lamps, as well as other types of lamps, there are many applications which include dimming the lamps and changing the color of the lamps. For example, it is often desirable for LED lamps in residential and commercial applications to be dimmable (i.e., have an adjustable brightness). Additionally, it may be desirable for LED lamps to have the capability to change colors when used in instrumentation, user interface displays, and other information-related applications. Further, display screens for information or entertainment applications make use of LED lamps that dim and/or change colors.
In some applications, drivers, which may be switch-mode drivers, linear drivers, or the like, are used to control the current to the lamp. In such setups, the average current, and therefore the brightness of the lamp, can be controlled based on receiving a control signal at the enable input of the driver. Often, these drivers have a limited input bandwidth, where the enable signal is not allowed to change quickly, the driver needing a minimum time to stabilize at each input level (e.g., on-time and off-time) between switching. For example, some drivers have a minimum stable time of 10 microseconds, or the like. This minimum stable time can be longer for high power LED lamp drivers.
Additionally, many control systems that feed a binary control signal to the drivers operate at much higher frequencies, often causing electro-magnetic compatibility (EMC) issues for the associated devices. On the other hand, the bit rate for a lamp control system needs to be high enough to help the human eye low-pass filter the lamp output, to avoid the appearance of lamp flickering. In other words, the bit rate needs to be higher than the flicker fusion threshold so that the light stimulus appears steady to the human eye due to persistence of vision. Further, a sufficiently high bit rate ensures that the system has an adequate overall bandwidth. In some applications, each of these requirements conflict with one another.